A heater used for toner fixing in a copier, a facsimile or the like, printing erasure or the like in a rewritable card reader, for example, is known. The heater causes a resistance heat-generating element formed on one surface of a substrate to generate heat using power supplied from a power supply electrode.
Generally, the resistance heat-generating element extends in a band shape along a longitudinal direction of an elongated substrate. The heater has a tendency that a temperature distribution is generated in the longitudinal direction of the substrate due to a difference between recording widths (lengths of recording sheets with respect to the longitudinal direction of the substrate) heated by the resistance heat-generating element. In a case where a temperature gradient that is generated between a central portion in the longitudinal direction of the substrate and both end portions thereof becomes large, there is a problem that cracks occur in the substrate due to the influence of thermal expansion.
As a countermeasure, on the substrate, a thermistor that measures temperature of the substrate is provided on the other surface thereof (a rear side of one surface on which the resistance heat-generating element is formed) with which a recording sheet, which is a heating target body, is in slidable contact. In the heater, there is a technique in which the temperature distribution in the longitudinal direction of the substrate is made uniform by controlling the amount of heat generated by the resistance heat-generating element, on the basis of the measurement result of the thermistor. A technique, in which a conductor that supplies power to the thermistor and the thermistor are formed on the other surface of the substrate using printing patterns, and a first connecting portion and a second connecting portion that are respectively connected to both ends of the conductor and the thermistor, are arranged along a lateral direction of the substrate, is known.
However, since the first connecting portion and the second connecting portion are formed as the respective printing patterns of the conductor and the thermistor overlap each other, a projection portion is formed in a thickness direction of the substrate. On the other hand, when the heater heats a recording sheet, the recording sheet is sent along the lateral direction of the elongated substrate. Thus, the recording sheet, which is indirectly in slidable contact with the other surface of the substrate through a fixing film, is continuously rubbed against two projection portions that correspond to the first connecting portion and the second connecting portion, which are arranged in a sending direction (in the lateral direction of the substrate) of the recording sheet, and thus, there is a concern that printing unevenness, so-called stripes (lines) in printing are easily generated.
A problem to be solved by the present disclosure is to provide a heater and an image forming apparatus capable of preventing connecting portions between a thermistor and a conductor from being continuously in slidable contact with a heating target body with which the connecting portions are indirectly in slidable contact.